Recently, with the growing speed of wireless communication, the frequency band of transmission signals has been becoming wider. In addition, in order to suppress degradation of signal quality, it is expected to suppress distortion to low levels over the wide band. For this reason, a complex intermediate frequency (IF) modulation method capable of implementing communication with low distortion in a wide band is employed in some wireless devices (particularly wireless base station devices). For example, in 3rd generation partnership project long term evolution (3GPP LTE)-advanced, where a bandwidth of 100 MHz is assumed, a complex IF modulation method is expected to be employed.
In the complex IF modulation method, an I-channel signal and a Q-channel signal are input to a digital-to-analog (D/A) converter, and then the D/A converter converts the I-channel signal and the Q-channel signal from digital signals to IF analog signals and outputs the signals. Then, a low pass filter (LPF) removes high frequency components of the I-channel signal and the Q-channel signal output from the D/A converter. Then, a quadrature modulator outputs a signal obtained by performing quadrature modulation of a carrier signal by using the I-channel signal and the Q-channel signal whose high frequency components have been removed by the LPF. Such techniques are disclosed in Japanese Laid-open Patent Publication No. 2008-228043, Japanese Laid-open Patent Publication No. 2008-199643, Japanese Laid-open Patent Publication No. 2002-151973, Japanese Laid-open Patent Publication No. 2007-019703, Japanese Laid-open Patent Publication No. 2007-208380, and Japanese Laid-open Patent Publication No. 2009-089269.